Dental bridges which are so anchored on distance members must be carefully adapted to the actual appearance of the jaw. The way in which this can be done is shown, for example, in Swedish Patent 446371 which describes how a positive working model of a lower or upper jaw provided with protruding distance members of this type can be produced. The impression system which is used there includes components such as impression tops and distance dummies which are fixed with the aid of guide pins.
A positive working model of the jaw obtained in this way is used by the dental technician for producing the finished dental prosthesis/dental bridge so that he does not have to carry out the time-consuming and complicated work involved in adapting the prosthesis directly in the patient's mouth. Instead, he works with a model of the patient's jaw. The production of the positive working model is facilitated with the aid of the components included in the impression system, namely the impression tops, distance dummies, gold cylinders and guide pins. It is known in the art how the various impression components are used and will therefore not be described in detail here. However, it will be noted that the impression technique and the production of the model comprise four stages:
the impression top is placed on the distance member,
the distance dummy is placed on the impression top,
the impression top is placed on the gold cylinder,
the gold cylinder is placed on the distance member.
In the first three stages a guide pin is used to fix the components to each other, while the gold cylinder is fixed on the distance member with the aid of a gold screw. Since the components always have a certain tolerance deficit, a degree of error is introduced during each of the four stages. The errors add up and can lead to stresses being built into the finished dental bridge.
To be more specific, the tolerance deficit results in the center of the various components ending up eccentric upon assembly. A guide pin is used which can facilitate centering, but the guide pin which has hitherto been used has a plane stop surface or contact surface which interacts with corresponding plane stop surfaces and guide edges of the respective component. Such a system gives a correct transfer vertically, but a certain error laterally since there is always a built-in play between the guide edge and guide bevel of the components.
It has also been proposed to make conical surfaces interact in an impression system, that is, to use a guide pin with conical guide surface which can interact with conical stop surfaces of the various components. Such a system should give a correct lateral positioning on account of the centering capacity of the guide pin, but it has hitherto required a new set of components with conical guide holes.